Over the past year we have pursued studies of B lymphocyte immunopathogenesis in HIV disease focused on 1) functional defects of B cells associated with ongoing viral replication and, 2) the role of B cells in trafficking virus. The importance of B cells in disseminating HIV in vivo was evaluated by macro (heteroduplex tracking assay) and micro (sequencing) molecular techniques to measure genetic diversity in various lymphoid tissue and peripheral blood compartments. HIV circulating on the surface of B cells was found to be closely related to virus found in productively infected CD4+ T cells. We also demonstrated that the amount of HIV virions bound to B cells was tightly linked to levels of HIV in the plasma. Regarding the deleterious effects of HIV plasma viremia on lymphocyte function, we have investigated both the responsiveness of B cells to CD4+ T cell help and the capacity of B cells to function as antigen presenting cells (APC). In normal subjects, expression of CD40 ligand on CD3/CD28-activated CD4+ T cells and availability of IL-2 dictated the capacity of B cells to respond to CD4+ T cell help. However, in HIV-infected viremic patients, B cell proliferation in response to CD4+ T cell help was reduced 2.5-fold when compared cross-sectionally to HIV-infected aviremic patients with matched CD4 counts and it was reduced 5-fold when compared longitudinally before and after reduction of plasma viremia in the same patient. Reduced proliferation of B cells was not due to reduced levels of CD40L on activated CD4+ T cells but rather, a strong correlation was found between B cell proliferation and induction of CD25 and other activation markers on B cells. Furthermore, when the APC function of B cells was investigated by triggering the B cell receptor (BCR) complex and/or CD40, B cells of viremic patients were found to be defective in their capacity to activate CD4+ T cells. Consistent with these findings, defects in B cell APC function correlated with reduced induction of B cell activation markers CD25, CD80 and CD86. Moreover, the importance of CD80/CD86 molecules in the APC function of B cells was demonstrated by using cells from normal donors and showing that CD4+ T cell activation was reduced to levels seen in viremic patients when CD80/CD86 on B cells was blocked from interacting with CD28 on CD4+ T cells. Finally, based on the observations that B cell dysfunction is tightly linked to levels of HIV plasma viremia, we have conducted gene microarray analyses on B cells isolated from HIV-viremic, HIV-aviremic, and normal subjects. The preliminary data indicate that B cells of HIV-viremic patients over-express genes induced by interferons and genes associated with terminal differentiation of B cells. Furthermore, a group of genes of the heat shock protein family were found to be down-regulated in both HIV-viremic and HIV-aviremic patients compared to normal donors.